This invention relates to novel methods and apparatus for making corrected custom molds of the human feet, from which orthopedic devices, or orthoses, for the foot can be fabricated. Such devices are now commonly referred to as "foot orthotics".
Knowledge of the mechanics of the human foot will help in understanding this invention. Made up of a complex array of twenty-six bones, the human foot performs two main functions, support and locomotion. Ideally, the foot functions as a tripod, supporting the body's weight on the heel and across the metatarsal arch. The foot is capable of a wide range of movement, including up and down, in and out, and side to side. Under stressed conditions, one of the most important of these movements is the side to side rotation of the foot, either to the outside ("supination") or to the inside ("pronation"). This rotation increases or decreases the height of the foot's arches, and if excessive, can put the foot in a weakened, unbalanced, condition. The foot is said to be in a "neutral" position when it is neither pronated nor supinated, i.e., when the heel bone is vertical and is directly in line with the talus bone above it. The neutral position provides good skeletal support for the body's weight.
However, it is known that knee position in relation to foot position is also an important factor in providing the maximum support for the body, particularly when the foot is in a full weight-bearing condition. As the foot pronates, the knee will tend to rotate to the inside, and conversely, as the foot supinates, the knee will tend to rotate to the outside. For the best balance and least stress, the knee should be aligned over the weight-bearing center of the foot. However, due to differences in individual structure, the knee may well be somewhat inside or outside its ideal position when the foot itself is placed in "neutral" (as defined above). Furthermore, putting the knee in its ideal position may leave the foot too far from neutral. In order to achieve the maximum skeletal support, one must balance both the position of the foot and the position of the knee. Failure to do so can place unnecessary stress on the foot, the knee and the rest of the body.
While so far we have only discussed the foot at rest, it is well known that activities which involve movement of the body, including walking, running, skiing, and skating, place very large stresses on the bones and joints of the leg and the foot. These stresses are large when the bones and joints of the foot are not in the proper position, and are maximized when the knee is additionally out of its proper alignment.
In the past, improper foot structure and position have sometimes been treated in part through custom-molded foot orthotics which fit into the shoes and which support the foot, or parts of the foot, in a "corrected" position. This corrective function of a foot orthotic distinguishes it from a mass-produced foot pad or other shoe insert designed strictly for comfort. Up to now, however, custom foot orthotics have been molded by archaic, complicated, time-consuming and expensive methods. For example, foot orthotics have often been molded (1) from actual foot measurements, (2) from a mold made of bandages coated with wet plaster which are wrapped around the foot until hard, and then cut off, (3) from a mold made by holding the foot motionless in wet plaster until hard and then cutting the mold open, and (4) from a directly molded heat-softening substance such as plastic. Therapeutic results with foot orthotics molded by these methods have tended to be inconsistent. First, by previous methods, it has usually been impossible to obtain a fully corrected mold of the foot, and thus the final device must be posted, or propped up with use of wedges on one side or the other, either in the forefoot, rear foot, or both, to achieve the desired result. Second, molding systems and/or techniques have rarely considered body structure above the foot, specifically the position of the knee in relationship to the foot. Even when the relationship between the position of the knee and the foot has been considered, no means of accurately and consistently measuring or determining the proper alignment between the position of the knee and the foot has existed, and no method or technique for molding a foot orthotic has been known which holds the foot and knee in that proper alignment during the molding operation. In addition, it now appears that foot orthotics for different activities, e.g. walking vs. running vs. skiing, may demand slightly differing positions for the bones of the foot and slightly differing adjustment between the knee and the foot. Such minute and subtle differences in position and alignment have been impossible to achieve accurately in foot orthotics molded by past methods and techniques.